Electrochemical Cell and Method of Making an Electrochemical Cell

ABSTRACT

Electrochemical test cells are made with precision and accuracy by adhering an electrically resistive sheet having a bound opening to a first electrically conductive sheet. A notching opening is then punched through the electrically resistive sheet and the first electrically conductive sheet. The notching opening intersects the first bound opening in the electrically resistive sheet, and transforms the first bound opening into a notch in the electrically resistive sheet. A second electrically conductive sheet is punched to have a notching opening corresponding to that of first electrically conductive sheet, and this is adhered to the other side of the electrically resistive sheet such that the notching openings are aligned. This structure is cleaved from surrounding material to form an electrochemical cell that has a sample space for receiving a sample defined by the first and second conductive sheets and the notch in the electrically resistive sheet.

This application claims the benefit of U.S. Provisional Application Ser.No. 60/521,555, filed May 21, 2004, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

This invention relates to electrochemical cells and methods of makingelectrochemical cells for detecting the presence of, measuring theamount of, and/or monitoring the level of one or more components in aliquid sample. The cells perform an electrochemical measurement byevaluating an electrochemical parameter (i.e., potential, current,resistance, etc) between two or more electrodes which are in contactwith a sample. Electrode sensors typically include a working electrodeand either a counter or a reference/counter (“reference”) electrode.

While use may be made of this invention in the chemical industry,especially where complex mixtures are encountered (e.g. in foodchemistry or biochemical engineering) it is of particular value inbiological investigation and control techniques. More particularly, itlends itself to animal or human medicine, and in particular to in vitromeasuring or monitoring of components in body fluids. For convenience,the invention will be described with reference to one such procedure,the determination of glucose within a human.

In order to effectuate a measurement of glucose in a human, a sample ofblood is drawn from a test subject and the sample mixed with a reagenttypically comprising an enzyme and a redox mediator. The chemistry usedin such a measuring device is typically:glucose+GOD_(ox)--->gluconolactone+GOD_(red)GOD_(red)+2 ferricyanide--->GOD_(ox)+2 ferrocyanide

-   -   where GOD_(ox) is the enzyme glucose oxidase in its oxidized        state, and GOD_(red) is the enzyme in a reduced state.        Ferricyanide ([Fe(CN)₆]³⁻) is the oxidized mediator which        oxidizes GOD_(red) so it can oxidize further glucose molecules.        Ferrocyanide ([Fe(CN)₆]⁴⁻) is the reduced form of the mediator        which transfers electrons to an electrode (thereby regenerating        ferricyanide). Thus, the generation of ferrocyanide (measured        electrochemically) indicates the concentration of glucose in the        sample. Other enyzmes, such as glucose dehydrogenase, have also        been used.

Because glucose monitoring for diabetics is preferably done severaltimes a day, and because each test using conventional apparatus for homeuse requires a finger stick to obtain blood or interstitial fluid, thedevelopmental pressure has been towards apparatus with ever increasingconvenience to the user and lower cost. As a result, electrochemicalcells with small sample test volumes have been disclosed. See, forexample U.S. Pat. Nos. 6,576,101; 6,551,494; 6,129,823 and 5,437,999. Asthe size of the sample cell becomes smaller, however, the percentagechange in electrode area and cell volume resulting from a small error inmanufacturing tolerance becomes greater. This is significant because themagnitude of the signal may depend on the electrode area and cellvolume. Thus, stricter manufacturing controls may be required in orderto achieve the necessary precision in cell size, but these strictercontrols are not compatible with the goal of reduced cost.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides a simple method forproducing electrochemical cells that is particularly applicable to themanufacture of cells with small and consistent sample volumes andelectrode areas. The resulting electrochemical cell comprises opposingfirst and second electrodes separated by an electrically resistivesheet. The method comprises the steps of:

-   -   (a) forming a first bound opening in an electrically resistive        sheet thereby forming a punched electrically resistive sheet;    -   (b) adhering the punched electrically resistive sheet to a first        electrically conductive sheet thereby forming a combined sheet,        wherein a first portion of a conductive surface of the first        electrically conductive sheet is exposed through the first bound        opening, and a second portion of the conductive surface of the        electrically conductive sheet is exposed either through a second        bound opening in the electrically resistive sheet or as an        extension beyond an edge of the electrically resistive sheet;    -   (c) punching a notching opening through the electrically        resistive sheet and the first electrically conductive sheet of        the combined sheet, wherein the notching opening intersects the        first bound opening in the electrically resistive sheet thereby        transforming the first bound opening into a notch in the        electrically resistive sheet, and punching a first contact area        opening through the second exposed portion of the electrically        conductive sheet visible to form a first electrical contact,        thereby forming a punched combined sheet;    -   (d) punching a second electrically conductive sheet with a punch        or punches to form an electrically conductive sheet having a        notching opening corresponding to that of the punched combined        sheet and a second contact area in the second electrically        conductive sheet, thereby forming an opposite electrode sheet;    -   (e) adhering the opposite electrode sheet to the electrically        resistive sheet portion of the punched combined sheet with an        electrically conductive surface facing the electrically        resistive sheet, said opposite electrode sheet being adhered        such that the notching opening corresponding to the notching        opening in the combined sheet is aligned with the notching        opening in the combined sheet, and the second contact area is        aligned with the second bound opening, thereby forming an        electrochemical sheet, and    -   (f) cleaving the electrochemical sheet thereby forming a spent        electrochemical sheet and a free electrochemical cell having a        sample space for receiving a sample defined by the first and        second conductive sheets and the notch in the electrically        resistive sheet, and first and second contact areas in        electrically-conductive contact with electrode portions of the        first and second conductive sheets exposed in the sample space        for connection of said first and second electrode portions with        a meter.

If appropriate for the test strip being made, reagent can be addedduring the construction of the test strip as described above.

In a preferred embodiment, both ends of the first major open area arecut in step (c) to form a sample space that is open at both ends, anddefined on the sides. One opening of the sample space is at the outeredge of the sample-collection tip of the device and the other openingadjoins a hole formed near the tip of the device.

The method of the invention provides numerous advantages over prior artmethods for the construction of electrochemical cells. First, the methodutilizes only a limited number of sheets of material that can be thesame size, and significantly larger than the cells as finally made.Second, the method of the invention does not require any printing orlithography techniques to define the sample space volume and theelectrode area or to form the electrode leads and connections. Third,because the significant dimensions of the device can be defined by diecutting or similar punching operations, both the accuracy and precisionof the manufacturing process is good using macroscopic processes. Thisallows the manufacture of electrochemical cells that operate with verysmall sample volumes, without substantial increase in manufacturingexpense. Fourth, electrochemical cells made using the method of theinvention have reduced electrode “edge” effects which reduce theaccuracy of the cell. Thus, the method of the present invention providesa cost effective and therefore disposable (single use) electrochemicalcell that demonstrates remarkable accuracy in measurements whilerequiring only a minimal amount of sample.

Practicing this method results in an electrochemical cell of simpleconstruction. Thus, in a further aspect of the invention, there isprovided an electrochemical cell having a sample-receiving end and aconnector end comprising, in sequence:

-   -   (a) a first substrate, having an unpatterned layer of conductive        material applied to a first surface thereof;    -   (b) an electrically-resistive middle layer, and    -   (c) a second substrate, having an unpatterned layer of        conductive material applied to a first surface thereof;    -   wherein the first surface of the first substrate and the first        surface of the second substrate are adhered to the electrically        resistive middle layer;    -   wherein the cell has a hole disposed near the sample receiving        end, but spaced away from the free edge of the cell, said hole        passing through the first substrate, the electrically resistive        middle layer, and the second substrate,    -   wherein the cell has a sample space, said sample space passing        through electrically resistive middle layer and being bounded on        opposing sides by the unpatterned conductive materials of the        first substrate and the unpatterned conductive material of the        second substrate and said sample space extending from the free        edge of the cell to the hole and being open at both ends. Where        appropriate to the cell being made, the electrochemical cell may        also include a reagent in the sample space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and B shows an isometric view of an electrochemical cellproduced by the method of this invention.

FIGS. 2A and B shows the sample receiving tip end and the sample spaceof a further embodiment of an electrochemical cell made in accordancewith the invention.

FIG. 3A-D show top views of embodiment of a sample receiving tip end.

FIGS. 4A-C show different embodiments of the connector end ofelectrochemical cells made in accordance with the invention.

FIG. 5 shows a schematic of the steps of the invention.

FIGS. 6A and B show embodiments of electrically resistive sheets havingbound openings.

FIG. 7 shows a detailed view of a combined punched sheet formed in themethod of the invention.

FIG. 8 shows a detailed view of a punched second conductive sheet formedin the methtod of the invention.

FIG. 9 shows a detailed view of a punched combined sheet useful in themethod of the invention.

FIG. 10 shows a view of a split electrode formed using the method of theinvention.

FIG. 11 illustrates the formation of a multi-test device using themethod of the invention.

FIGS. 12A and B show cross sections through a multi-test device formedas in FIG. 11.

FIG. 13 illustrates the formation of another embodiment of a multi-testdevice using the method of the invention.

FIG. 14 shows another multi-cell test device.

FIG. 15 shows another multi-cell test device.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with an embodiment of the present invention a method isprovided for manufacturing of electrochemical cells comprising the stepsof:

-   -   (a) punching one or more bound openings into an electrically        resistive sheet thereby forming a punched electrically resistive        sheet, said one or more bound openings defining a first and a        second major open areas,    -   (b) adhering the punched electrically resistive sheet to a first        electrically conductive sheet thereby forming a combined sheet,        wherein a conductive surface of the first electrically        conductive sheet is visible through the one or more openings in        the punched electrically resistive sheet,    -   (c) punching a notching opening through the electrically        resistive sheet and the first electrically conductive sheet of        the combined sheet, wherein the notching opening intersects the        first major area in the electrically resistive sheet thereby        transforming the first major open area into a notch in the        electrically resistive sheet, and punching a first contact area        opening through the portion of the electrically conductive sheet        visible through the second major open area of the electrically        resistive sheet to form a first electrical contact, thereby        forming a punched combined sheet;    -   (d) punching a second electrically conductive sheet with a punch        or punches to form an electrically conductive sheet having a        notching opening corresponding to that of the punched combined        sheet and a second contact area in the second electrically        conductive sheet, thereby forming an opposite electrode sheet;    -   (e) adhering the opposite electrode sheet to the electrically        resistive sheet portion of the punched combined sheet with an        electrically conductive surface facing the electrically        resistive sheet, said opposite electrode sheet being adhered        such that the opening corresponding to the notching opening in        the combined sheet is aligned with the notching opening in the        combined sheet, and the second contact area is aligned with the        second bound opening, thereby forming an electrochemical sheet,        and    -   (f) cleaving the electrochemical sheet thereby forming a spent        electrochemical sheet and a free electrochemical cell having a        sample space for receiving a sample defined by the first and        second conductive sheets and the notch in the electrically        resistive sheet, and first and second contact areas in        electrically-conductive contact with electrode portions of the        first and second conductive sheets exposed in the sample space        for connection of said first and second electrode portions with        a meter.        Definitions

Numerical values in the specification and claims of this applicationshould be understood to include numerical values which are the same whenreduced to the same number of significant figures and numerical valueswhich differ from the stated value by less than the experimental errorof conventional measurement technique of the type described in thepresent application to determine the value.

As used in the specification and claims of this application, thefollowing terms are used and should be understood as follows:

The term “analyte” as used in the specification and claims of thisapplication means a component of a sample to be measured. Non-limitingexamples of specific analytes include glucose, hemoglobin, cholesterol,and vitamin C.

The term “redox mediator” as used in the specification and claims ofthis application means a chemical species, other than the analyte, thatis oxidized and/or reduced in the course of a multi-step processtransferring electrons to or from the analyte to an electrode of theelectrochemical cell. Non-limiting examples of mediators include:

-   -   ferricyanide    -   [FeIII(CN)5(ImH)]²⁻    -   [FeIII(CN)5(Im)]³⁻    -   [RuIII(NH3)5(ImH)]³⁺    -   [RuIII(NH3)5(Im)]²⁺    -   [FeII(CN)5(ImH)]³⁻    -   [RuII(NH3)5(Im)H]²⁺    -   [(NC)5FeII(Im)RuIII(NH3)5]⁻    -   [(NC)5FeIII(Im)RuIII(NH3)5]⁰    -   [(NC)5FeII(Im)RuII(NH3)5]²⁻    -   Ferrocene (Fc) and derivatives including but not limited to:    -   Ferrocene monosulphonate    -   Ferrocene disulphonate    -   FcCO₂H    -   FcCH₂CO₂H    -   FcCH:CHCO₂H    -   Fc(CH₂)₃CO₂H    -   Fc(CH₂)₄CO₂H    -   FcCH₂CH(NH₂)CO₂H    -   FcCH₂SCH₂CH(NH₂)CO₂H    -   FcCH₂CONH₂    -   Fc(CH₂)₂CONH₂    -   Fc(CH₂)₃CONH₂    -   Fc(CH₂)₄CONH₂    -   FCOH    -   FcCH₂OH    -   Fc(CH₂)₂OH    -   FcCH(Me)OH    -   FcCH₂O(CH₂)₂OH    -   1,1′-Fc(CH₂OH)₂    -   1,2-Fc(CH₂OH)₂    -   FcNH₂    -   FcCH₂NH₂    -   Fc(CH₂)₂NH₂    -   Fc(CH₂)₃NH₂    -   1,1′-Me₂FcCH₂NH₂    -   FcCH₂NMe₂    -   (R)-FcCH(Me)NMe₂    -   (S)-FcCH(Me)NMe₂    -   1,2-Me₃SiFcCH₂NMe₂    -   FcCH₂NMe₃    -   FcCH₂NH(CH₂)₂NH₂    -   1,1′-Me₂FcCH(OH)CH₂NH₂    -   FcCH(OH)CH₂ NH₂    -   FcCH:CHCH(OH)CH₂NH₂    -   Fc(CH₂)₂CH(OH)CH₂NH₂    -   FcCH₂CH(NH₂)CH₂OH    -   FcCH₂CH(CH₂NH₂)CH₂OH    -   FcCH₂NH(CH₂)₂OH    -   1,1′-Me₂FcCHOCONHCH₂    -   FcCH(OH)(CH₂)₂NH₂    -   1,1′-Me₂FcCH(OH)CH₂NHAc    -   FcB(OH)₃    -   FCC₆H₄OPO₃Na₂

Osmium II and Osmium III tris(phenanthroline) (i.e. Os-phen) complexesincluding but not limited to:

-   -   Os(4,7-dmphen)₃    -   Os(3,4,7,8-tmphen)₃    -   Os(5,6-dmphen)₃    -   Os(bpy)₃Cl₂    -   Os(5-mphen)₃    -   Os(5-Cl-phen)₃    -   Os-(5-NO2-phen)₃    -   Os(5-phphen)₃    -   Os(2,9-dm-4,7-dpphen)₃    -   and isostructural ruthenium complexes including but not limited        to:    -   Ru(4,7-dmphen)₃    -   Ru(3,4,7,8-tmphen)₃    -   Ru(5-mphen)₃    -   Ru(5,6-dmphen)₃    -   Ru(phen)₃    -   [Ru(4,4′-diNH₂-bipy)₃]²⁺    -   Osmium III and Osmium III tris(bipyridyl) complexes (i.e.        Os(bpy)₃) including but not limited to:    -   Os(bpy)₃    -   Os(dmbpy)₃    -   and related ruthenium complexes, e.g.:    -   Ru(bpy)₃    -   Ru(4,4′-diNH₂-bpy)₃    -   Ru(4,4′-diCO₂Etbpy)₃    -   Osmium II and Osmium III bis(bipyridyl) (i.e. Os(bpy)₂)        complexes with other ligands including but not limited to:    -   Os(bpy)₂dmbpy    -   Os(bpy)₂(HIm)₂    -   Os(bpy)₂(2MeHIm)₂    -   Os(bpy)₂(4MeHIm)₂    -   Os(dmbpy)₂(HIm)₂    -   Os(bpy)₂Cl(HIm)    -   Os(bpy)₂Cl(1-MeIm)    -   Os(dmbpy)₂Cl(HIm)    -   Os(dmbpy)₂Cl(1-MeIm)    -   and related ruthenium complexes, e.g.:    -   Ru(bpy)₂(5,5′diNH₂-bpy)    -   Ru(bpy)₂(5,5′diCO₂Etbpy)    -   Ru(bpy)₂(4,4′diCO₂Etbpy)    -   where Et is ethyl, bpy is bipyridyl, dmbpy is dimethyl        bipyridyl, Melm is N-methyl imidazole, MeHIm is methyl        imidazole, Him is imidazole, phen is phenanthroline, mphen        ismethyl phenantholine, dmphen is dimethyl phenanthroline,        tmphen is tetramethyl phenanthroline, dmdpphen is dimethyl        diphenyl phenanthroline, phphen is phenyl phenanthroline. In        addition, it is understood that reduced or oxidized forms of        these mediators may be used, either alone or in combination with        each other.

Patents relating to particular mediators include U.S. Pat. Nos.4,318,784, 4,526,661, 4,545,382, 4,711,245, 5,589,326, 5,846,702,6,262,264, 6,352,824, 6,294,062, 4,942,127, 5,410,059, 5,378,628,5,710,011, and 6,605,201 which are incorporated herein by reference.

The term “an opening having a rectilinear cross-section” as used in thespecification and claims of this application is an opening having fourstraight sides. The reference to straight sides refers merely to sidesthat are not obviously curved when viewed, and does not imply acriticality of perfect linearity from the punching process. Non-limitingexamples of rectilinear cross-section openings are trapezoids,parallelograms, squares and rectangles. The corners of the rectilinearopenings are desirably rounded. Openings of this shape are preferredbecause the straight edges have less error in cutting, and the roundedcorners are less prone to tearing.

The term “bound opening” refers to an opening which is surrounded by thematerial of the electrically resistive sheet, where there is no directconnection between the opening and the periphery of the resistive sheet.As described in greater detail below, a bound opening may have a singlemajor open area, for example an opening having a rectilinearcross-section, or it may have more than one major open area connected bya generally narrower connecting portion.

The term “major open area” refers to a portion of a bound opening inwhich either the sample space or the connectors of an electrochemicalcell will be formed.

The term “opposing electrodes” refers to electrodes disposed ondifferent substrates used in the formation of the sample cell, such thatthey are disposed in different planes on the top and bottom (or on thetwo sides) of a cell, such that movement of charge carriers occurs in adirection generally perpendicular to the plane of the electrodes.“Opposing electrodes” are thus different from side-by-side electrodes inwhich an electrode pair is disposed on a common surface in a commonplane, and the movement of charge carriers is generally parallel to theplane of both electrodes.

The term “punching” as used in the specification and claims of thisapplication refers to the act of cutting through a sheet of material ina direction substantially perpendicular to the major surface. The term“substantially” in this case recognizes that there may be slightmanufacturing deviations from absolutely perpendicular, but that theseshould be minimized to avoid top to bottom inconsistency in thedimensions of the openings created. Punching can be performed using adie cutting apparatus or other apparatus that physically cuts the layersinto the desired shape. Laser cutting can also be employed where heatgeneration and/or evolution of volatiles is not a concern. Chemicaletching through the materials might also be employed.

The term “unpatterned layer of conductive material” refers to adeposition of conductive material, for example by painting, sputtering,evaporation, screen printing, chemical vapor deposition, or electrolessdeposition onto the surface of a material without any defined patterningto define the electrode area. Patterning may be used for the contactpads or connector tracks, however, a wholly unpatterned layer may beemployed for all of the conductive elements, and this is preferred sincefewer manufacturing steps are involved. The unpatterned or whollyunpatterned layer is desirably a uniform coating, although randomscratches, pits or other defects that may occur as a result of handlingor manufacturing processes do not render a conductive materialpatterned.

Electrochemical Cells

The method of the present invention is used to make electrochemicalcells. FIG. 1A shows schematic representation of such a cell. The cellis formed from a bottom layer 130, a top layer 131, and a middle layer132. The top and bottom layers are electrically conductive, at least onthe surfaces facing the middle layer 132. In preferred embodiments, thetop and bottom layers 130, 131 are an insulating substrate onto which aconductive layer has been coated. As more clearly shown in FIG. 1B inwhich the top layer 131 has been removed, the middle layer 132 has anotch 133 formed in one edge. The notch 133, and the top and bottomlayers 130, 131 together define a space into which sample is receivedwhen the electrochemical cell is in use. The volume of this space isthus defined by the thickness of the middle layer 132 and the dimensionsof the notch. The electrochemical cell also has contact areas 134 and135 that are attachable to a meter to provide an electrical connectionbetween the meter and the portion of the top and bottom layers 130, 131that are exposed in the space for receiving a sample.

The middle layer 132 is an electrically resistive material whichisolates the conductive layers, and prevents electrical conductivitybetween the electrically conductive top and bottom layers 130, 131,unless they are connected via a sample disposed in the space forreceiving a sample. Non-limiting examples of suitable materials for useas this layer include polyimide, polyester, polyethylene terephthalate(PET), polycarbonate, glass, fiberglass or other nonconductive materialsthat provide the desired support. The middle layer 132 suitably has athickness of 500 to 50 μm. Thicker materials can be used where largersample volumes are acceptable. Thinner materials can be used, but maycreate difficulties in handling, and increased difficulty in drawingsample into the finished cell since this thickness determines onedimension of the sample space. In a preferred embodiment of the presentinvention, the sample space volume is less than 5 μl and more preferablyless than 1 μl. In specific embodiments of the invention, the volume ofthe sample space is 500, 300, 200, 100 or 50 nl.

The conductive portion of top and bottom layers 130, 131 is selectedconsistent with the specific analyte that the electrochemical cell isintended to detect. Specific examples of suitable conductive electrodematerials include gold, carbon, silver, palladium, and platinum. Theconductive material used in the top and bottom layers 130, 131 may bethe same or they may be different from one another. In a preferredembodiment of the present invention the conductive material is gold. Theconductive portion of the top and bottom layers is suitably a thincoating on one surface of an insulating substrate sheet. Materials usedfor the middle layer 132 may be used as this substrate as well.

Depending on the analyte to be detected, the electrochemical cell mayinclude a reagent composition disposed within the space for receiving asample. In the case of an electrochemical cell for the detection ofglucose, this reagent composition suitably comprises an enzyme effectiveto oxidize glucose, for example glucose oxidase, and a redox mediator,for example ferricyanide. Reagent compositions for this purpose areknown in the art, for example from U.S. Pat. No. 4,711,245 to Higgins etal. and U.S. Pat. No. 5,437,999 to Diebold et al., which areincorporated herein by reference. A particular embodiment of the reagentcomprises glucose oxidase and ferricyanide.

In addition to its electrochemical function, the reagent composition,when present, may assist in overcoming the hydrophobicity of the samplespace, so that blood or other aqueous sample can be drawn into the spaceby the hydrophilicity of the reagent. Where a reagent is not used,surface treatment of the sample volume to reduce hydrophobicity and tofacilitate sample introduction may be indicated, for example with Tritonor other surfactants.

FIGS. 2A-B shows the sample receiving tip end and the sample space of afurther embodiment of an electrochemical cell made in accordance withthe invention. In FIG. 2A, the device is fully assembled. The samplespace 22 extends from the tip 23 of the device to a hole 24. The lengthl of the sample chamber is on the order of 1 mm, for example from 1.5 mmto 0.5 mm, although longer lengths can be used to make sample spaceswith larger volumes. FIG. 2B shows the tip region of FIG. 2A with thetop layer removed. The conductive surface 25 of the bottom layer 26 isvisible in the bottom of the sample space 22. The sample space 22 isdefined on the bottom by the conductive surface 25 of sheet 26 and onthe sides by the resistive sheet 27. The ends of the sample space areopen at the end of the device and to the hole 24.

FIG. 3A shows a top view of a variation of the sample receiving tipregion of FIG. 2A. In this case, at least the distal portion (i.e, theportion towards the tip end) of the hole 34 is shaped to becomplementary to the shape of the tip end. The term “complementary”means that the profile of the front of the strip 36 is identical to theprofile of the front of the hole 38, the former being displaced from thelatter by movement in the direction of the length of the sample space orchannel 22 This configuration is desirable to maintain a consistentvolume for the sample space, and a consistent area of the electrodeseven when the alignment of the sample space with the rest of the deviceis imperfect. (FIG. 3B). This configuration also allows multiple samplespaces in the tip of the device with the same benefits, as shown inFIGS. 3C and 3D.

FIGS. 4A-C show different embodiments of the connector end ofelectrochemical cells made in accordance with the invention. In FIG. 4A,connector tab 41 extends from the end of the device as an extension ofthe first conductive layer 42 with the conductive surface facingdownwards in the orientation shown. Connector tab 43 extends from theend of the device as an extension of the second conductive layer 44 withthe conductive surface facing upwards in the orientation shown.Electrically resistive layer 45 is shown between the conductive layers42, 44. FIG. 4B shows an alternative embodiment in which twoperipherally located tabs, 141, 141′ extend from the top conductivelayer and one centrally located tab 46 extends from the bottomconductive layer. FIG. 4C shows a further alternative embodiment inwhich two peripherally located tabs, 141, 141′ extend from the topconductive layer and two centrally located tabs 146, 146′ extend fromthe bottom conductive layer.

Method of the Invention

In accordance with the method of the invention, an electrochemical cellas described above is constructed by punching one or more bound openingsinto an electrically resistive sheet thereby forming a punchedelectrically resistive sheet having at least one bound opening. Boundopenings are preferred in the method of the invention because suchopenings have greater dimensional stability than a notch cut into theedge of a sheet, and therefore provides less manufacturing variation inthe size of the space for receiving a sample. In an embodiment of thepresent invention the bound openings in the electrically resistive sheetare of “rectilinear cross-section.”

The punched electrically resistive sheet is adhered to a firstelectrically conductive sheet thereby forming a combined sheet in whicha conductive surface of the first electrically conductive sheet isvisible through the first and second openings in the punchedelectrically resistive sheet. The specific material used to accomplishthe adherence is not critical, although thick layers of adhesive thatcould contribute variation in the size of the space for receiving asample are not desirable. A preferred example of an electricallyresistive sheet coated with adhesive is one made with apressure-sensitive acrylic adhesive such as ARCARE 7841 made byAdhesives Research. Other examples of commercially available adhesivesapplied to polyester substrates are made by 3M: 3M #444, 3M # 443 and 3M#1512. Selection of the adhesive product is driven, at least in part, bythe desired height of the sample space which is defined by the substrateplus the adhesive coatings. The adhesive is suitably applied over theentire electrically resistive layer to form a uniform coating, as isavailable in commercial double sided “tapes.” Heat sealing might also beused as could techniques such as ultrasonic welding.

The next step is punching a notching opening through the electricallyresistive sheet and the first electrically conductive sheet of thecombined sheet. The notching opening transversely intersects the firstbound opening in the electrically resistive material, i.e., it cutsthrough two sides, preferably two opposed sides in a rectilinear firstbound opening of the first bound opening, thereby transforming the firstbound opening into a notch in the electrically resistive sheet. Thisresults in the formation of a first electrode area that is defined bythe notching punch of the combined sheet and by the notch in theelectrically resistive sheet. In addition, a first electrical contact isformed by punching through the portion of the electrically conductivesheet visible through the second bound opening of the electricallyresistive sheet to form a first electrical contact, thereby forming apunched combined sheet. In a preferred embodiment, a single punchingstep is used to form both the notching opening and the first electricalcontact.

A second electrically conductive sheet is punched with a punch orpunches to form an electrically conductive sheet having a notchingopening corresponding to that of the punched combined sheet, therebyforming an opposite electrode sheet having a second electrode area and asecond contact area in the second electrically conductive sheet. As usedin the specification and claims of this application, an electricallyconductive sheet having a notching opening corresponding to that of thepunched combined sheet is one in which the opening in the resultingopposite electrode sheet will substantially align with the openings andnotches of the punched combined sheet when the second electricallyconductive sheet is adhered to the punched combined sheet. Indeed, forease of manufacture, the same punch or punches (i.e., either the samephysical unit, or one with identical dimensions) can be used to form theopposite electrode sheet as was/were used to form the punched combinedsheet. The invention does not, however, exclude embodiments in which thedimensions of the opposite electrode sheet are intentionally made to bedifferent so as to provide working and counter electrodes of differentdimensions.

An optional step of adding a reagent may be performed. For ease ofmanufacturing the desired reagent may be added to the punched combinedsheet, wherein the notch in the electrically resistive material servesas a reservoir for holding the added reagent. Alternatively the reagentmay be added to first or second electrically conductive material or botheither prior to or after being punched. In yet another embodiment noreagent is added during the production of the electrochemical cell. Insuch a case, if a reagent is desired it may be added directly to thesample within the electrochemical cell or prior to the sample'sintroduction to the cell.

If desired, different reagents may be applied on the two opposingelectrodes. Because of the small separation of the electrodes, diffusionof the reagents is rapid when sample is present, but this approachallows two reactive reagents to be kept apart until sample is added. Forexample, if the presence of an enzyme inhibitor is being determinedthrough loss of enzyme activity, it would be undesirable to have asingle reagent containing enzyme and substrate since they could reactduring the deposition process. In particular, a phosphatase such asalkaline phosphate can be used to cleave a phosphate substrate toproduce an electrochemically detectable product (such as p-aminophenol).This reaction can be inhibited by excess phosphate, arsenates andshellfish toxins, making it useful in a variety of analyte-specificdevices. Separate reagent depositions might also be used to separate anenzyme from a buffering agent, so that the enzyme was only at a correctpH for reaction after sample addition and combination of the reagents.

After the formation of the corresponding opening and the secondelectrical contact in the second electrically conductive sheet, theresulting opposite electrode sheet is adhered to the electricallyresistive sheet portion of the punched combined sheet with anelectrically conductive surface facing the electrically resistive sheet.The opposite electrode sheet is adhered such that the punched opening inthe opposite electrode sheet corresponding to the notching opening inthe combined sheet is aligned with the notching opening in the combinedsheet, and the second contact area is aligned with the second boundopening of the combined sheet. This results in the formation of anelectrochemical sheet in which a second electrode area is defined on theopposite electrode sheet by the notch in the electrically resistivesheet and the dimensions of the punch of the second electricallyconductive sheet.

Finally, the electrochemical sheet is cleaved to form a spentelectrochemical sheet from the surrounding material and a freeelectrochemical cell having a space for receiving a sample defined bythe first and second electrodes and the notch in the electricallyresistive material, and first and second contact areas inelectrically-conductive contact with the first and second electrodes forconnection of said first and second electrodes with a meter. This stepcan be performed on one cell at a time, on one sheet of cells at a time,or on multiple cells or sheets in a combined operation.

It will be appreciated that multiple cells can be formed from each sheetof material by formation of multiple sets of punches adjacent to oneanother. It will also be appreciated that multiple cells can be formedimmediately adjacent to each other, so that no excess material is leftbetween them when they are cleaved. Multiple strips can also be formedfrom a single sheet in a “nose to tail” or “nose to nose and tail totail” arrangement such that punching of a single bound opening forms thenose of one strip and the tail of the next strip at once, or nose andnose, or tail and tail.

In an embodiment of the present invention a sample is drawn into theelectrochemical cell by the hydrophilic nature of the dried, solublereagent. To prevent an air lock that would inhibit filling, a vent isoften required for venting of gases from the cell as the sample is drawninto the cell. For such a case the punched combined sheet may furthercomprise a vent opening punched through the electrically resistive sheetand the first electrically conductive sheet, wherein the vent opening isaligned with the notch in the electrically resistive sheet to form apassageway for air that connects to the interior of the space forreceiving a sample.

Alternatively the vent opening may be punched through the secondelectrically conductive sheet of the combined sheet, wherein the ventopening is aligned in the assembled cell with the notch in theelectrically resistive sheet to form a passageway for air that connectsto the interior of the space for receiving a sample. In yet anotherembodiment both vent openings may be punched. A sample may be drawn intothe sample area through a vent or through the opening between theelectrically conductive sheets.

In a preferred embodiment of the invention as illustrated in FIGS. 2A,2B and 3, the vent hole 24, 34 is formed such that it transversely cutsthrough the notch and thereby defines the proximal end (i.e, the inwardend) of the sample space 22. In this case, it will be appreciated thatthe proximal “vent hole” may actually act as the point of sampleintroduction with the distal opening serving the function of a vent. Avent hole of this type may be formed through the entire device (i.e,through the first conductive sheet, the electrically resistive sheet andthe second conductive sheet), or through only one of the conductivesheets and the electrically resistive sheet.

A specific embodiment of the method of the invention is shown in FIG. 5.The following steps illustrate a process for the production of twoelectrochemical cells. It will be appreciated, however, that the processmay be altered to produce one cell at a time, or to make more than twoelectrochemical cells using the same steps in a mass productionoperation.

Step One: An electrically resistive sheet is provided. The electricallyresistive sheet 51 is coated with an adhesive on both major surfacesthereof.

Step Two: As shown in detail in FIG. 6A, two registration holes 61 areprovided to the electrically resistive sheet 51 from step one formanufacturing alignment and do not become part of the final device. Theelectrically resistive sheet 51 is placed into a die assembly (notshown) wherein the die assembly aligns the electrically-resistive sheetvia the two registration holes. The electrically resistive sheet 51 isthen punched thereby forming a punched electrically-resistive sheet 52with two large and two small openings through the sheet. The largeopenings 62 are the openings through which the electrical connectorswill be formed. The small openings 63 are the openings across which thenotching opening and the vent opening will be made to define the samplespace. FIG. 6B shows an alternative construction in which the conductivelayer extends beyond the edges of the resistive layer, and the connectoris formed in this extension. Thus, only one bound opening, which isinvolved in the formation of the sample space, is needed.

Step Three: The punched electrically resistive sheet 52 is then adheredto a first electrically conductive sheet 53 thereby forming a combinedsheet 54. The electrically conductive sheet has at least one surfacecoated with a conductor, for example gold, which faces the punchedelectrically resistive sheet 52, and includes two registration holes inalignment with the registration holes of the electrically resistivesheet 52. Once the combined sheet 54 is formed, the conductive surfaceof the first electrically conductive sheet 53 is visible through theopenings in the punched electrically resistive sheet 52.

Step Four: The combined sheet 54 is punched, thereby forming a punchedcombined sheet 55. FIG. 7 shows this punched combined sheet 55 ingreater detail. The punched combined sheet 55 is cut such that both theproximal and distal ends of the rectangular opening 63 are cut off,leaving the start of a generally rectangular/square sample space 71. Thepunch of step four also defines a first electrical connector 72 throughwhich the electrode formed from the first electrically conductive sheetmay be electrically connected with a measuring device.

Step Five: A reagent 513 is added to the punched combined sheet 55 overthe sample space 71, thereby forming a reagent sheet 56. For a glucosesensor, the reagent that is added to the punched combined sheet 55suitably comprises glucose oxidase and a redox mediator comprisingferricyanide. Preferably, the mediator is added in a liquid carrier thathas a volume sufficient to fill at least 50%, and more preferably agreater portion of the sample space. This results in a coating of themediator higher on the walls of the sample space, and therefore closerto the second electrode. This decreases the time for mediator to reachthe second electrode during use, and thus improves the response time ofthe device.

Step Six: Two registration holes are provided to a second sheet of anelectrically conductive material 57. The two registration holes are formanufacturing alignment and do not become part of the final device.Electrically conductive sheet 57 is placed into a die assembly (notshown) and is punched, thereby forming an opposite electrode sheet 58.The punch used defines the top electrode for the sample space. Thus, asshown in FIG. 8, punched opening 81 defines a device tip 82 and a venthole 83 having the same shape as those in the punched combined sheet 55.The punch also defines a second connector area 84, for connecting theelectrode formed from the second sheet of electrically conductivematerial. The punch forming the second connector area 84 need not be thesame as the punch forming connector area 72. What is desired is theultimate of two sets of accessible contacts that do not make electricalcontact one with another.

The second electrically conductive sheet 57 is suitably of the samematerial and construction of the first electrically conductive sheet 53,although it may be made of a different material, or include a label.

Step Seven: Opposite electrode sheet 58 is adhered to reagent sheet 56from step five thereby forming an electrochemical sheet 59, wherein theregistration holes of the opposite electrode sheet align with theregistration holes of the reagent sheet. The conductive portion ofopposite electrode sheet 58 is in contact with the electricallyresistive sheet of the reagent sheet 6. This step results in thedefinition of the sample space, bounded by the two electricallyconductive sheets on the top and bottom, and the electrically resistivesheet on the sides, and having openings at each end.

Step Eight: Electrochemical sheet 59 from step seven is cleaved therebyforming a spent electrochemical sheet 510 and two free electrochemicalcells 511 and 512. It may be appreciated how the steps of thisembodiment may be altered to result in a process that produces more thanor less than two electrochemical cells.

FIG. 9 shows a mechanism for dividing the portion of the conductivecoating that does not form the electrode surface within the sample spaceto form two legs. A stylus 91 is dragged along the conductive surface 92of the gold 58 to form a non-conductive line or gap 93 which divides theconductive surface from the vent hole 94 to the end of the strip at theconnectors 95. This non-conductive line or gap 93 can be formed afterdefining the connectors and vent hole by punching, or before this, usingthe registration holes as a guide to ensure that scribed line isproperly positioned. In the latter case, the scribe line may extend intothe region that will be romoved by puching. The non-conductive line forthe first sheet must be formed before the electrically resistive sheetis adhered to the first conductive sheet (Step 3). Other methods forforming the non-conductive line or gap 93 besides simply dragging astylus over the surface include the use of cutting wheels which may passthrough the entire conductive layer, laser ablation and chemicaletching.

When this format is used to punch one or both of the conductive sheets,the result is a cell which can be readily tested for electricalcontinuity as part of a quality control procedure as illustrated in FIG.10. FIG. 10 shows just the electrode layer of a cell if punchingpatterns and a scribed line as shown in FIG. 9 are used. The location ofthe sample space 122 is shown in dashed lines. If the electricalconnection (for example via a conductivity measurement) is assessedbetween connectors 101 and 102, a good connection will be determinedprovided that there is no damages to the conductive sheet that extendsall the way across either leg or the loop portion of electrode layer.For example, a scratch 103 or 104 would be detected as a fail, while ascratch such as 105 would not. Since connection between the electrodeportion over the sample space 122 and either one of the connectors 101or 102 is sufficient for a valid test result, this provides an easilyachieved, non-destructive form of quality control which is actually morerigorous than the requirements of the operative device. The twointermediate connector tabs could also be formed by scribing, as shownin FIG. 9 intermediate along the length of this surface, withoutrequiring a cut to configure the tabs.

The method of the invention can also be used to make multi-test celldevice. FIG. 11 illustrates a first method for accomplishing thisresult, in which two test cells are stacked one on top of the other. Inthis method, two punched combined sheets 1101 and 1102 are formed asdescribed above. Reagent is added to each punched combined sheet 1101,1102 consistent with the analyte to be tested. The reagents added tosheets 1101 and 1102 may be the same or they may be different to providefor simultaneous testing of two analytes. Punched combined sheets 1101and 1102 each have an adhesive inner surface 1103, 1103′ and are adheredvia this surface to an intermediate punched sheet 1104 formed from anelectrically insulating material coated on both sides with a conductivelayer. After cleaving the cell from the sheet, the result is a testdevice that has two stacked test cells. FIG. 12A shows a cross sectionthrough the resulting multi-cell device at a point remote from thesample space and vent hole. FIG. 12B shows a cross section through theresulting multi-cell device as a point intersecting the sample spaces1222, 1222′ and vent hole 1224. In each figure, the conductive surfacesare reflected by a wavy line. Because of the small size of the testcells, and the proximity of the openings, sample can be easilyintroduced into both cells concurrently.

FIG. 13 illustrates an alternative embodiment of a method for making amulti-test cell device. In this embodiment, two or more adjacent samplespaces are formed. As depicted in FIG. 13, two openings are formed inplace of the single first bound opening used to define the sample spacein the embodiments described above. In the specific embodiment shownFIG. 13 A, two co-linear openings 1301, 1302 perpendicular to the longaxis of the device are formed in the electrically resistive sheet. Whenthe combined strip is punched along the dashed lines to form the devicenose 1304 and vent hole 1305, the ends of both openings are cleaved,creating two sample spaces. In this configuration, the sample spaces aresuitably filled from the vent hole. A cut or scribe along the dottedline 1306 is made in the electrically conductive sheet prior to assemblyto provide electrical isolation for the two sample spaces. It will beappreciated that the same result could be achieved with one elongatedopening that combined openings 1301 and 1302, and extended across thevent hole area between. Further, it will be appreciated that therelative specific positions of the openings formed in this embodimentare not critical, and that they need not be co-linear (e.g. FIG. 3C)provided that isolated electrical connections can be made to each samplespace.

In a further embodiment of the method of the invention, multi-testdevices can be made using a combination of the methods shown in FIGS. 11and 12 with the method illustrated in FIG. 13. In this embodiment, theresulting device may have one or more cells in each stacked level.

In yet a further embodiment of the invention of the cell of FIG. 13, bydisplacing the openings 1301, 1302, and providing separate vent holes,two sample spaces can be formed in such a way that only one space isfillable from the outside edge, and the other only from the inside edge.In the absence of cut 1306, it does not matter which of the samplespaces was filled. This creates greater user convenience, since thesample collection point (the manner in which the strip is used) does notimpact the result. Filling of both spaces can be distinguished fromfilling of only one based on determinations of effective electrode area,for example as described in US Patent Publication U.S. 2005-0069892 A1and U.S. patent application Ser. No. 10/907,813 filed Apr. 15, 2005,which are incorporated herein by reference.

FIGS. 14 and 15 show two other embodiments of multi-cell test devices.In FIG. 14, four sample spaces 1401 are formed, all of which areaccessed via a common surface. Since filling (or partial filling) of anyor all of these is sufficient to obtain a measurement, thisconfiguration reduces the need to align a particular portion of thedevice tip with a blood/fluid droplet 1402. In FIG. 15, six samplespaces 1501 are aligned in a ring around a hexagonal multi-strip andextend from the outside of the ring to vent spaces 1502. The devices areseparated by scribe lines 15-3 and have connector tabs 1504 directed tothe center axis. In FIG. 15, only one conductive layer and the spacerlayer are shown. A top layer with a conductive surface would completethe device with the other electrode and its associated connector tab(s).

Thus, it can be seen that the method of the invention providesflexibility in the formation of electrochemical test cells that includemultiple sample spaces. These sample spaces may be coplanar, in whichcase they can be arranged in parallel, in a nose-to-tail arrangement,like the spokes of a wheel, in a wheel or in any other desiredconfiguration. The sample spaces may also occupy multiple planes.

1. A method of manufacturing an electrochemical cell, wherein theelectrochemical cell comprises opposing first and second electrodesseparated by an electrically resistive sheet, wherein the methodcomprises the steps of: (a) forming a first bound opening in anelectrically resistive sheet thereby forming a punched electricallyresistive sheet; (b) adhering the punched electrically resistive sheetto a first electrically conductive sheet thereby forming a combinedsheet, wherein a first portion of a conductive surface of the firstelectrically conductive sheet is exposed through the first boundopening, and a second portion of the conductive surface of theelectrically conductive sheet is exposed either through a second boundopening in the electrically resistive sheet or as an extension beyond anedge of the electrically resistive sheet; (c) punching a notchingopening through the electrically resistive sheet and the firstelectrically conductive sheet of the combined sheet, wherein thenotching opening intersects the first bound opening in the electricallyresistive sheet thereby transforming the first bound opening into anotch in the electrically resistive sheet, and punching a first contactarea punch through the second exposed portion of the electricallyconductive sheet visible to form a first electrical contact, therebyforming a punched combined sheet; (d) punching a second electricallyconductive sheet with a punch or punches to form an electricallyconductive sheet having a notching opening corresponding to that of thepunched combined sheet and a second contact area in the secondelectrically conductive sheet, thereby forming an opposite electrodesheet; (e) adhering the opposite electrode sheet to the electricallyresistive sheet portion of the punched combined sheet with anelectrically conductive surface facing the electrically resistive sheet,said opposite electrode sheet being adhered such that the notchingopening corresponding to the notching opening in the combined sheet isaligned with the notching opening in the combined sheet, and the secondcontact area is aligned with the second bound opening, thereby formingan electrochemical sheet, and (f) cleaving the electrochemical sheetthereby forming a spent electrochemical sheet and a free electrochemicalcell having a sample space for receiving a sample defined by the firstand second conductive sheets and the notch in the electrically resistivesheet, and first and second contact areas in electrically-conductivecontact with electrode portions of the first and second conductivesheets exposed in the sample space for connection of said first andsecond electrode portions with a meter.
 2. The method of claim 1,further comprising as part of forming the opposite electrode, the stepof punching a vent opening through the second electrically conductivesheet of the combined sheet, wherein the vent opening is aligned in theassembled cell with the notch in the electrically resistive sheet toform a passageway to the interior of the space for receiving a sample.3. The method of claim 1, further comprising, as part of forming thepunched combined sheet, the step of punching a vent opening through theelectrically resistive sheet and the first electrically conductive sheetof the combined sheet, wherein the vent opening is aligned with thenotch in the electrically resistive sheet to form a passageway to theinterior of the space for receiving a sample.
 4. The method of claim 3,further comprising as part of forming the opposite electrode, the stepof punching a vent opening through the second electrically conductivesheet of the combined sheet, wherein the vent opening is aligned in theassembled cell with the notch in the electrically resistive sheet toform a passageway to the interior of the space for receiving a sample.5. The method of claim 1, wherein the vent opening intersects with anend of the first major open area and together with the notching openingdefines the length of the sample space.
 6. The method of claim 1,further comprising the step of adding a reagent to the space forreceiving a sample.
 7. The method of claim 6, wherein the reagent isadded to the notch in the punched combined sheet prior to formation ofthe electrochemical sheet.
 8. The method of claim 7, wherein the reagentcomprises an enzyme and a redox mediator.
 9. The method of claim 8,wherein the enzyme is glucose oxidase.
 10. The method of claim 1,wherein the first and second electrically conductive sheets comprisegold.
 11. The method of claim 1, wherein the bound openings in theelectrically resistive sheet are of rectilinear cross-section.
 12. Themethod of claim 1, wherein the electrically resistive sheet and thefirst and second electrically conductive sheets are each provided withaligned registration holes for manufacturing alignment, saidregistration holes being located in the portion of the sheets that iscleaved off as the spent electrochemical sheet, such that they do notbecome part of the final device.
 13. The method of claim 1, wherein theelectrically resistive sheet has a thickness, and the notch hasdimensions such that the space for receiving a sample has volume of lessthan 1 μl, preferably less than 0.5 μl.
 14. The method of claim 1,wherein two bound openings are formed in the resistive sheet.
 15. Themethod of claim 1, wherein the opposite electrode has two opposingconductive surfaces, and wherein both sides of the opposite electrodeare adhered to a combined punched sheet to form a device with twostacked sample receiving spaces.
 16. The method of claim 1, wherein aplurality of bound openings are formed in the electrically resistivesheet, whereby a plurality of coplanar sample receiving spaces areformed.
 17. An electrochemical device made by the method of claim
 1. 18.An electrochemical device having a sample-receiving end and a connectorend comprising, in sequence: (a) a first substrate, having anunpatterned layer of conductive material applied to a first surfacethereof; (b) an electrically-resistive middle layer, and (c) a secondsubstrate, having an unpatterned layer of conductive material applied toa first surface thereof; wherein the first surface of the firstsubstrate and the first surface of the second substrate are adhered tothe electrically resistive middle layer; wherein the device has a holedisposed near the sample receiving end, but spaced away from the freeedge of the device, said hole passing through the first substrate, theelectrically resistive middle layer, and the second substrate, whereinthe device has a first sample space, said first sample space passingthrough electrically resistive middle layer and being bounded onopposing sides by the unpatterned conductive materials of the firstsubstrate and the unpatterned conductive material of the secondsubstrate and said sample space extending from the free edge of thedevice to the hole and being open at both ends.
 19. The device of claim18, further comprising a reagent disposed within the sample space. 20.The device of claim 19, wherein the reagent comprises an enzyme and aredox mediator.
 21. The device of claim 20, wherein the enzyme isglucose oxidase.
 22. The device of claim 18, wherein the conductivematerial on the first substrate comprises gold.
 23. The device of claim22, wherein the conductive material on the second substrate comprisesgold.
 24. The device of claim 18, wherein the middle layer has athickness of 50 to 500 μm.
 25. The device of claim 18, wherein thesample space has a volume of less than 1 μl, preferably less than 500nl, and more preferably of 100 to 300 nl.
 26. The device of claim 18,further comprising a second sample space formed in a stackedconfiguration relative to the first sample space.
 27. The device ofclaim 18, further comprising an additional sample space formed in acoplanar location relative to the first sample space.